Contributions are welcomed. Please see the following site for guidelines:
http://sass-lang.com/community#Contribute
The Sass repository has three primary development branches, each of which tracks a different line of releases (see versioning below). Each branch is regularly merged into the one below: stable into next, next into master.
The stable branch is the default—it‘s what GitHub shows if you go to sass/sass, and it’s the default place for pull requests to go. This branch is where we work on the next patch release. Bug fixes and documentation improvements belong here, but not new features.
The next branch is where we work on the next minor release. It‘s where most new features go, as long as they’re not breaking changes. Very occasionally breaking changes will go here as well—see exceptional breakages below for details.
The master branch is where we work on the next major release. It's where breaking changes go. We also occasionally decide that a non-breaking feature is big enough to warrant saving until the next major release, in which case it will also be developed here.
Ideally, pull requests would be made against the appropriate branch, but don't worry about it too much; if you make a request against the wrong branch, the maintainer will take responsibility for rebasing it before merging.
Tests for changes to the Sass language go in sass-spec so that other implementations (E.g. libSass) can be tested against the same test suite. The sass-spec repo follows a “trunk development” model in that the tests there test against different version of the Sass language (as opposed to having branches that track different Sass versions). When contributing changes to Sass, update the Gemfile to use sass-spec from a branch or fork that has the new tests. When the feature lands in Sass, the committer will also merge the corresponding sass-spec changes.
The documentation of sass-spec explains how to run sass-spec and contribute changes. In development, Change the Gemfile(s) to use the :path option against the sass-spec gem to link your local checkout of sass and sass-spec together in one or both directions.
Changes to Sass internals or Ruby Sass specific features (E.g. the sass-convert tool) should always have tests in the Sass test directory following the conventions you see there.
Sometimes it won‘t be possible to merge a new feature into next or master immediately. It may require longer-term work before it’s complete, or we may not want to release it as part of any alpha releases of the branch in question. Branches like this are labeled feature.#{name} and stay on GitHub until they're ready to be merged.
Not all features pan out, and not all code is a good fit for merging into the main codebase. Usually when this happens the code is just discarded, but every so often it‘s interesting or promising enough that it’s worth keeping around. This is what experimental branches (labeled experimental.#{name}) are for. While they're not currently in use, they contain code that might be useful in the future.
Usually Sass doesn't have the development time to do long-term maintenance of old release. But occasionally, very rarely, it becomes necessary. In cases like that, a branch named stable_#{version} will be created, starting from the last tag in that version series.
Starting with version 3.5.0, Sass uses semantic versioning to indicate the evolution of its language semantics as much as possible. This means that patch releases (such as 3.5.3) contain only bug fixes, minor releases (such as 3.6.0) contain backwards-compatible features, and only major releases (such as 4.0.0) are allowed to have backwards-incompatible behavior. There are exceptions, but we try to follow this rule as closely as possible.
Note, however, that the semantic versioning applies only to the language‘s semantics, not to the Ruby APIs. Although we try hard to keep widely-used APIs like Sass::Engine stable, we don’t have a strong distinction between public and private APIs and we need to be able to freely refactor our code.
Sometimes the old way of doing something just isn‘t going to work anymore, and the new way just can’t be made backwards-compatible. In that case, a breaking change is necessary. These changes are rarely pleasant, but they contribute to making the language better in the long term.
Our breaking change process tries to make such changes as clear to users and as easy to adapt to as possible. We want to ensure that there‘s a clear path forward for users using functionality that will no longer exist, and that they are able to understand what’s changing and what they need to do. We've developed the following process for this:
Deprecate the old behavior in stable. At minimum, deprecating some behavior involves printing a warning when that behavior is used explaining that it‘s going to go away in the future. Ideally, this message will also include code that will do the same thing in a non-deprecated way. If there’s a thorough prose explanation of the change available online, the message should link to that as well.
If possible, make sass-convert (also in stable) convert the deprecated behavior into a non-deprecated form. This allows users to run sass-convert -R -i to automatically update their stylesheets.
Implement the new behavior in master. The sooner this happens, the better: it may be unclear exactly what needs to be deprecated until the new implementation exists.
Release an alpha version of master that includes the new behavior. This allows users who are dissatisfied with the workaround to use the new behavior early. Normally a maintainer will take care of this.
Because Sass's syntax and semantics are closely tied to those of CSS, there are occasionally times when CSS syntax is introduced that overlaps with previously-valid Sass. In this case in particular, we may introduce a breaking change in a minor version to get back to CSS compatibility as soon as possible.
Exceptional breakages still require the full deprecation process; the only change is that the new behavior is implemented in next rather than master. Because there are no minor releases between the deprecation and the removal of the old behavior, the deprecation warning should be introduced soon as it becomes clear that an exceptional breakage is necessary.